There are a considerable number of known techniques associated with surface characterization. For example, U.S. Pat. Nos. 3,804,534 and 4,918,321 teach methods and apparatus directed toward such characterization. These prior art systems, however, tend to be highly sophisticated, typically including means whereby very detailed characteristics associated with a wide range of surface types may be analyzed and displayed, often resulting in an expensive end product.
However, there are certain applications where a fast but accurate true/false type of determination is required instead of such a detailed analysis. One such application is associated with the processes involved with the bonding to glass surfaces. For example, prior to the bonding of mechanical fasteners to automobile window glass, the region of glass to be bonded is necessarily microscopically roughened, with an etchant such as silene forming a thin primer coating. This primer coating etches the glass so that the bonding attaches securely to the glass and remains intact even under the stresses of daily window use. If the primer is not applied correctly such mechanical clips may appear to be bonded properly, but will be lacking in strength, resulting in premature failure.
As such, prior to the process of bonding these mechanical components to the glass surface, it is desirable to have a fast and accurate test of surface roughness to ensure that the primer has been applied sufficiently and in the correct locations, whether on one or both sides of the glass panel. Such an application is not served by an expensive and complex piece of analytical equipment. Since the characteristics of the glass surface before and after the application of the etchant are well known, it should be unnecessary to perform a detailed analysis, and it is certainly unnecessary to provide an image of the surface. All that the individual testing the surface requires is a fast but accurate indication of whether the surface in a region of interest has been prepared to a predetermined extent, or whether it remains smooth and untreated.